Short-wave radioreceiver



Feb. 4, 1930. R. s. OHL 1,745,376

SHORT WAVE RADIORECEIVER Filed Dec. 51, 1924 INVENTOR l. 51 01% BY 1.

ATTORNEY Patented Feb. 4-, 1930.

UNITED STATES mi .azu'r RUSSELL s. OHL, on NEW YORK, N. Y., nssrcnoafroAnmncm rsmsnoan Ann TELEGRAPH COMPANY, A OORYORATION on" YORK SHORT-WAVEmmionscmvsa Application filed December 31, 1924. Serialms. 759,697.

r This invention relates to radio receiving systems and particularly toa systemof that type which is adapted to receive radio signalstransmitted by Oscillations having a wave length of the Order of 2 to 8meters.

- Radio receiving systems that have been devised and used for thereception of signals transmitted by oscillations of relatively longwaves, as, for example, of the Order of 300 to 500 meters, are not welladapted for receiving extremely short waves of the order of 2 to 3meters. There are several causes for such inability or inefliciency ofthe long wave receivers when used for short wave reception. Theprincipal cause of failure resides in the capacitance of the variousparts of the long wave receiver which becomes a serious factor 3 meters,which system is free from the detin receiving signals of the frequencyof 100,000 kilocycles. I

One of the objects of this inventionis to provide a receiving circuitfor a short wave signaling system, of the Order of from 2 to rimentaleffects present in long'wave receivers when used for short wavereception.

This and other objects of the invention will be apparent from thefollowing description when read in connection with the attached drawing,of which Figure 1 shows schematically a form of embodiment of theinvention, and Fig. 2 is a detail of Fig. 1 illustrating the mode ofwinding the tuning inductance shown in Fig. 1.

1 In Fig, 1, the antenna 1, which is made up of a straight wiredisconnected from the aground, is coupled to the receiving circuit bymeans of the single turn 2 in the middle of the wire constituting theantenna. The total length of the wire should be about One-half the wavelength of the signals to be received.

Thereceiving circuit, which is a detecting circuit,comprises atuninginductance made up of the coils f3 and 4, which coils are inductivelyrelated each to the other, and to the single turn 2 Of the antenna. Thecoil 3 is connected with the plate 5 of the vacuum 1 tube 6, and thecoil ,4 with the grid 7 of the said tube. The filament 8 is activated bythe source 9 of direct current, the magnitude of which is controlled bythe resistance 10. A

Ivariahle condenser 11- isconnectedbetween the-terminal- 16 of coil 3'and the terminallf ofcoil 4. A resistance 12 of low capacity isconnected between-the filament 8' and the terminal 17 of coil 4, thesaid resistance acting as a grid leak to the detector tube. Gonnectedbetween thesa-i'd filament and the terminal 16 of coil '8 is the signalindicating circuit comprising a receiver 14, a source of plate voltage13 and an inductance 15. This inductance should have lowdistributed'capacity and should be of-very high impedance for thefrequencies used, thus serving as a choke coil to keep the highfrequencies out of the low frequency circuit. .The manner ofconstructing the tuning inductance 8% is clearly shown in Fig. 2. Eachcoil should be made of heavy copper wire, for example, :of No. 14: B.hard drawn wire so as t O be self-supporting. The turns should be evenlyspaced and the coils shouldbewoiind inthc same direction. v The mannerin which the circuit functions asa detector willbe apparent byconsidering the detail shownin Fig. 2. In this figure, the capacitybetween the grid 7 and the plate 5 is represented by the dottedcondenser 18. The resonant circuit may be traced from the terminal 16through the coil "3 to the plate '5, thence through the -capacit'yrepresented by 18 to the grid 7, thence through the coil 41- to theterminal 17, andfinallyth-rough the variable condenser 11 to theterminal 16.- The condenser 11 should be adj-usteduntil' a condition ofresonance is created at the signaling frequency. The incomingoscillations upon which the signal to be detected is superimposed will.be impressed by the turn 2 of the antenna upon the tuning inductance.Thesetoscillations will be detected in the receivin'g areal-cane theesultant signal will be impressed upon the signal in 1i cating device 13connected w'iththeplate-fiiament cir- "cuit. I i

As will beseen, the detector circuit is or the #95 type-having a;condenser in 'the'giid lead, and

a grid leak. The detecting action obtains by usin the pro erties of thevacuum take, operating. it uponthe curved portion of the gridwoltage,grid-current characteristic and 5100 plate-current characteristic. Thismethod of detecting signals is well known to those skilled in the artand is described in various text-books so that it seems unnecessary todescribe it herein.

As an aid in working the invention heretofore described, it may bestat-ed that in a radio receiver intended for the'reception of waves ofabout two meters, the variable condenser 11 should preferably have amicromecember,192 l.

, RUSSELL S. OHL.

ter adjustment and should be of maximum capacity of about 45 mmf, and ofminimum capacity of not more than about 5 mmf. This permits about 200%variation in wave length.

The resistance 12should be a low capacity 2 megohm element, and, asstated, the choke coil 15 should be of low capacity and high impedance.the reception ofwaves of 2 or 3 meters since other wave lengths may bereceived by apparatus embodying my invention.

A receiving system of the type described should preferably be elevatedabove theearth When this is done, the leads supplying the current toIthefilament of the tube should also have a high impedance choke coil ineach in order to suppress the transmission therethrough of the highfrequencies.

While this invention hasbeen disclosed as embodied in a particularform,it isto be understood that itis capable of embodiment in other formswithout departing from the spirit and scope of the appended claims.

What is claimed is: I

1. An oscillation detector for short waves comprising a vacuum tubehaving a plate, a grid and a filament, two mutually inductive coils oneconnected with the plateand the other with the grid of the said tube, asource of plate potentialeffectively connected with "the plate coil, agrid leak resistance connect- Theiinvention is not limited to 1 inordervtoimprove thereceiving efiiciency.

condenser having one side connected with the plate circuit between theplate coil and the said source of potential, andhaving its other 'sideconnected with the grid circuit-between the grid coil and the grid leakresistance.

1 ;2.' An oscillation detector for short waves 7 comprising a vacuumtube having a plate, a grid and a filament, a circuit connecting thesaid plate and the said filament including'an inductance coil, a sourceof platepotential, an

indicating device and a choke coil operative I to suppress highfrequency oscillations, a cirlcuit connectingsaidgrid and. said filamentincluding an" inductance coil and a grid leak I "circuit, the point ofconnection with each circuit-beingat or. near..-that terminal ofthe inresistance, theicoilsof the plate circuit and 1

